PAEK polymers, including in particular poly(etheretherketone) (PEEK), poly(etherketone) (PEK) and poly(etherketoneketone) (PEKK) polymers are well known for their exceptional balance of technical properties, namely high melting point, good thermal stability, high stiffness and strength, good toughness and especially excellent chemical resistance. Therefore, PAEK have potential for a wide variety of uses, and their favorable properties class them with the best of the engineering polymers. For example, PEEK polymers have found increasing use in the manufacturing of high temperature and fire resistant films since PEEK has good elongation and good flexibility in thin sections such as films, or for coating of wires since PEEK has good flame resistance, being self extinguishing with very low smoke.
It is also widely recognized that certain uses of PAEK polymers, in particular in thin films and in wire coatings, require the material also have enhanced electrical insulating properties and low tendency to arc track. However, PAEK polymers are rather susceptible to arc tracking.
Polytetrafluoroethylene (PTFE) polymers, while known for their thermal stability, high melting temperature, chemical inertness and lubricity (low coefficient of friction and non-stick character), excellent electrical insulation properties, very low dielectric constant and including a very low tendency to arc track when used in wire coatings, they are also known for their non-melt-fabricability, i.e. they cannot be fabricated by such usual melt-fabrication technique as melt extrusion, including injection molding. Instead, (PTFE) is processed by such non-melt flow techniques as paste extrusion (fine powder type of (PTFE)) and compression molding (granular type of (PTFE)) into strong articles, the strength of which can be augmented by sintering.
(PTFE) resins of lower molecular weight (typically, 50,000 to 700,000 as opposed to standard (PTFE), generally having mass exceeding 2,000,000) and having lower melt viscosity (MV) are known in the art.
While these (PTFE) are melt flowable, the much lower molecular weight deprives them of strength, whereby articles molded from this low MV (PTFE) by melt extrusion break upon handling. Thus, although melt flowable, the low MV (PTFE) is not melt fabricable.
The use of low MV (PTFE) with non-fluorinated thermally stable polymers such as PAEK polymers has already been discussed in the prior art.
For example, U.S. Pat. No. 6,013,719 discloses PAEK/(PTFE) compositions which have the utility of being melt fabricable into improved articles. In particular, blends of PEKK with certain low MV (PTFE) polymers, more precisely with ZONYL® MP 1600 (PTFE) powder having a MFR 17 g/10 min at 372° C., a melting peak temperature of 325° C. measured according to ASTM D4894 and a particle size distribution of about 12 μm measured by Laser Microtrac, has been described in the examples.
JP-A 58-160,346 discloses a PAEK/(PTFE) resin composition which has outstanding sliding characteristics and comprises a thermoplastic aromatic polyetherketone such as PEEK, as a base material, 10 to 40% by weight of polytetrafluoroethylene which has a mean particle size of less than 20 μm as a fluorocarbon polymer and 10 to 40% by weight of a carbon fiber. It is stated that a high heat distortion temperature (HDT) and a high limiting PV value are obtained by the above resin composition. The thermoplastic aromatic poly(ether ketone) can have an intrinsic viscosity (IV) of between 0.7 and 2.6 (dL/g), measured at 25° C. on a solution of 0.1 g of polymer in 100 ml H2SO4 with a density of 1.84 g/cm3.
U.S. Pat. No. 5,131,827 discloses a PEEK/(PTFE) composition suitable for scroll compressor parts containing 60 parts by weight of PEEK, 30 parts by weight of a SiC whisker, 10 parts by weight of carbon fiber, 7 parts by weight of (PTFE), in particular Fluon® L150 J (PTFE), said (PTFE) having a average particle diameter of 9 μm, and 3 parts by weight of Boron Nitride (BN).
EP 1 454 963 A1 discloses the synthesis of a low-molecular weight (PTFE) which is characterized by a number averaged particle size of 5 μm, a melt viscosity of 2.0×105 poises (2.0×104 Pa·s) measured at 380° C. and a melting point of 327° C. Resin compositions containing PEEK (Victrex PEEK 450G) and 0.025 and 0.005% mass of said low-molecular weight (PTFE), relative to the total mass of PEEK and (PTFE), are exemplified in examples 8 and 9. Said PEEK/(PTFE) resins are for use as a molding material.
However, there is still a shortfall in the art for PAEK/(PTFE) compositions especially suitable for the manufacture of thin PAEK-based films and wire coatings, thus possessing low tendency to arc track and very low dielectric constant thereby providing enhanced electrical insulation properties, but also possessing a combination of high performance properties including high temperature performance, mechanical strength, chemical resistance, high friction and wear resistance, good flame resistance, low smoke and moreover offering superior processability/flow capabilities, especially offering an improved melt and coating extrusion. There is thus still a high need for thin PAEK-based films having a reduced tendency to tearing and/or forming holes during melt manufacturing and/or having improved surface appearance (e.g. having a lower amount of surface defects) and/or having an increased smoothness. There is also still a high need for thin PAEK-based wire coatings, having a reduced tendency to tearing and/or surface fracturing during coating extrusion.